The present invention relates to a VSB receiver, and more particularly, to a VSB receiver for receiving a terrestrial digital broadcasting signal which is subjected to vestigial side-band (VSB) modulation and is transmitted.
In recent years, in the video broadcasting field, the broadcasting form has been changing from an analog form to a digital form in order to provide a high-quality video to a viewer, as is well known. The broadcasting is being digitized with respect to not only broadcasting by a satellite wave which has already been partially put to practical use but also broadcasting by a ground wave. In the United States and Europe, for example, the digitization of broadcasting by a ground wave is being currently put to practical use.
As a digital modulation system used in terrestrial digital broadcasting, various systems have been currently devised. As one of the systems, the ATSC (Advanced Television System Committee) standard for subjecting a signal to multi-valued VSB (octal VSB or hexadecimal VSB) modulation and transmitting the modulated signal has been employed in the United States.
A receiver for receiving the terrestrial digital broadcasting is feasible by being constructed similarly to a receiver basically employed in satellite digital broadcasting or the like, provided that it performs digital demodulation corresponding to digital modulation to which a signal has, been subjected. With respect to a receiver for receiving a signal which has been subjected to multi-valued VSB modulation (hereinafter referred to as a VSB receiver), a general I configuration is described in a document entitled xe2x80x9cGUIDE TO THE USE OF THE ATSC DIGITAL TELEVISION STANDARD (Doc. A/54)xe2x80x9d issued by ATSC.
FIG. 20 illustrates an example of the configuration of a VSB receiver described in the above-mentioned document issued by ATSC. In FIG. 20, the VSB receiver described in the document comprises a tuner 201, a digital demodulation portion 202, a waveform equalizer 203, an error-correcting circuit 204, a transport decoder 205, a video decoder 206, and an audio decoder 207.
The tuner 201 receives a signal which has been subjected to VSB modulation. The digital demodulation portion 202 subjects the signal received by the tuner 201 to digital demodulation, and converts the received signal into a digital video signal. The waveform equalizer 203 corrects the distortion or the like of a signal waveform which occurs in a transmission path or the like. The error-correcting circuit 204 subjects the signal waveform whose distortion or the like has been corrected to error correction. The transport decoder 205 separates a video signal and an audio signal which have been transmitted in multiple. The video decoder 206 decodes the separated video signal. The audio decoder 207 decodes the separated audio signal.
It is generally considered that an automatic gain control (hereinafter denoted by an AGC) circuit and a clock regenerating circuit which are indispensable in processing a signal are naturally included as constituent elements in the digital demodulation portion 202, which is not written clearly in the VSB receiver shown in FIG. 20.
The AGC circuit is a circuit whose gain is controlled by a negative feedback loop such that the amplitude of a predetermined reference signal always enters a predetermined level in order to eliminate the effect of the attenuation or the like of a signal on the transmission path, as is well known. Further, the clock regenerating circuit is a circuit whose gain is controlled by a negative feedback loop such that the clock frequency of the received signal and the clock frequency of the receiver coincide with each other (synchronized) in order to regenerate a clock for giving judgment timing of each data (symbol) of a digital signal as is well known.
Each of the AGC circuit and the clock regenerating circuit is operated in order to cause a signal to be controlled to converge into a predetermined value by the negative feedback loop. Accordingly, the loop gain of each of the circuits affects a time period required until the convergence processing is completed, that is, a time period required from the time when a video signal is received until a video is outputted onto a screen. Therefore, the loop gain of each of the AGC circuit and the clock regenerating circuit is fixed to a most suitable value previously determined at which the convergence processing is performed at high speed and accurately.
Meanwhile, the terrestrial digital broadcasting differs from satellite digital broadcasting in that it is necessary to consider that a ghost disturbance is created in the transmission path. Against the ghost disturbance, it is considered that in the above-mentioned VSB receiver, the effect of a ghost can be removed in the processing in the waveform equalizer 203.
When it is considered that the AGC circuit and the clock regenerating circuit are included in the configuration of the VSB receiver, however, the following problems arise depending on a method of setting the loop gain of each of the circuits.
First, consider a case where the loop gain of the AGC circuit is set to a large value.
In this case, the speed of AGC processing following a feedback signal is increased, so that the loop gain of the AGC circuit converges at high speed. In this case, however, the value of the result of AGC detection (an AGC voltage) is liable to be changed. When a ghost disturbance exists in the received signal, therefore, the result of the AGC detection is changed by a ghost component. Therefore, an error occurs in signal processing in the waveform equalizer 203 in the succeeding stage, resulting in a degraded ghost removal capability.
The configuration of the waveform equalizer 203 described in the above-mentioned document is taken as an example, to describe the cause of errors occurring in the signal processing in the above-mentioned case. FIG. 21 is a block diagram showing the configuration of the waveform equalizer 203 described in the above-mentioned document. FIG. 22 is a diagram for explaining the reason why judgment in the waveform equalizer 203 is erroneous.
The waveform equalizer 203 calculates an error signal on the basis of an output of a feedback filter and an output passing through a slicer, and calculates each filter coefficient on the basis of the error signal. The filter coefficient is gradually changed such that a ghost is removed, and the value is hardly changed after the ghost is removed. That is, the waveform equalizer 203 calculates a filter coefficient on the basis of an error between each data and a reference value in a region including the data. Consequently, the waveform equalizer 203 calculates, with respect to data in a +5 region (xe2x97xaf mark in FIG. 22), an error between the data and the value of +5, and calculates a filter coefficient on the basis of the error. When data originally existing in the +5 region is moved into a +7 region (▾ mark in FIG. 22) by a ghost disturbance, however, the waveform equalizer 203 calculates, with respect to the data, an error between the data and the value of +7, and calculates an incorrect filter coefficient on the basis of the error.
Similarly, consider a case where the loop gain of the clock regenerating circuit is set to a large value.
In this case, the speed of clock regeneration processing following a feedback signal is increased, so that the loop gain of the clock regenerating circuit converges at high speed. When a ghost disturbance exists in the received signal in this case, however, the clock regeneration processing sensibly responds to a ghost component (the clock frequency is liable to vary). Accordingly, jitter occurs in a regenerated clock in the VSB receiver, so that an error occurs in the received signal.
Then, consider a case where the loop gains of the AGC circuit and the clock regenerating circuit are respectively set to small values.
In this case, in the AGC circuit, the speed of AGC processing following a feedback signal is decreased, resulting in an enhanced ghost removal capability. On the other hand, in the clock regenerating circuit, the speed of clock regeneration processing following a feedback signal is decreased, so that an accurate clock can be regenerated without causing jitter. In this case, however, a time period required until the loop gain of each of the circuits has converged as described above, that is, a time period required from the time when a video signal is received until a video is outputted onto a screen is lengthened.
Therefore, an object of the present invention is to provide a VSB receiver in which a reduction of a time period required until convergence is completed and an improvement of a ghost disturbance removal performance are made compatible with each other in an AGC circuit, and a reduction of a time period required until convergence is completed and accurate clock regeneration are further made compatible with each other in a clock regenerating circuit.
The present invention has the following features in order to attain the above-mentioned object.
A first aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation; and
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant,
the automatic gain control part switching the loop filter to a wide band until the segment synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal.
Preferably, as in a second aspect,
the loop filter is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a third aspect,
the loop filter is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
As described above, according to the first to third aspects, the loop filter in the automatic gain control part is switched to a wide band until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a narrow band in order to improve the ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance.
A fourth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation; and
automatic gain control part whose loop gain is feedback-controlled through again detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant,
the automatic gain control part switching the gain of the amplifier to a large value until the segment synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal.
Preferably, as in a fifth aspect,
the amplifier is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a sixth aspect,
the amplifier is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
As described above, according to the fourth to sixth aspects, the amplitude gain of the automatic gain control part is switched to a large value until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a small value in order to improve a ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance.
A seventh aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the segment synchronizing signal detected by the segment synchronization detection part,
each of the automatic gain control part and the clock regeneration part switching the loop filter to a wide band until the segment synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal.
Preferably, as in an eighth aspect,
the loop filter in each of the automatic gain control part and the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
each of the automatic gain control part and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a ninth aspect,
the loop filter in each of the automatic gain control part and the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
each of the automatic gain control part and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a tenth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to respectively control the bandwidths of the loop filters.
Preferably, as in an eleventh aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to respectively control the bandwidths of the loop filters.
As described above, according to the seventh to eleventh aspects, the loop filter in each of the automatic gain control part and the clock regeneration part is switched to a wide band until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a narrow band in order to improve a ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A twelfth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the segment synchronizing signal detected by the segment synchronization detection part,
each of the automatic gain control part and the clock regeneration part switching the gain of the amplifier to a large value until the segment synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal.
Preferably, as in a thirteenth aspect,
the amplifier in each of the automatic gain control part and the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
each of the automatic gain control part and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a fourteenth aspect,
the amplifier in each of the automatic gain control part and the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
each of the automatic gain control part and the clock regeneration part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a fifteenth aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to respectively control the gains of the amplifiers.
Preferably, as in a sixteenth aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to respectively control the gains of the amplifiers.
As described above, according to the twelfth to sixteenth aspects, the amplitude gain of each of the automatic gain control part and the clock regeneration part is switched to a large value until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a small value in order to improve a ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A seventeenth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the segment synchronizing signal detected by the segment synchronization detection part,
the automatic gain control part switching the loop filter to a wide band until the segment synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal, and the clock regeneration part switching the gain of the amplifier to a large value until the segment synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the segment synchronization detecting signal.
Preferably, as in an eighteenth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a nineteenth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a twentieth aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a twenty-first aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier.
As described above, according to the seventeenth to twenty-first aspects, the loop filter in the automatic gain control part and the amplitude gain of the clock regeneration part are respectively switched to a wide band and a large value until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being respectively switched to a narrow band and a small value in order to improve a ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A twenty-second aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
segment synchronization detection part for detecting the segment synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the segment synchronizing signal detected by the segment synchronization detection part such that the level of the segment synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the segment synchronizing signal detected by the segment synchronization detection part,
the automatic gain control part switching the gain of the amplifier to a large value until the segment synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the segment synchronization detecting signal indicating the presence or absence of the detection of the segment synchronizing signal, and the clock regeneration part switching the loop filter to a wide band until the segment synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the segment synchronization detecting signal.
Preferably, as in a twenty-third aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a twenty-fourth aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the segment synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a twenty-fifth aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a twenty-sixth aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the segment synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the segment synchronization detecting signal, to control the bandwidth of the loop filter.
As described above, as in the twenty-second to twenty-sixth aspects, the amplitude gain of the automatic gain control part and the loop filter in the clock regeneration part are respectively switched to a large value and a wide band until the segment synchronizing signal is detected such that a time period required for the detection is shortened, while being respectively switched to a small value and a narrow band in order to improve a ghost disturbance removal performance after the segment synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the segment synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A twenty-seventh aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation; and
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant,
the automatic gain control part switching the loop filter to a wide band until the field synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal.
Preferably, as in a twenty-eighth aspect,
the loop filter is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter,
Preferably, as in a twenty-ninth aspect,
the loop filter is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
As described above, as in the twenty-seventh to twenty-ninth aspects, the loop filter in the automatic gain control part is switched to a wide band until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a narrow band in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance.
A thirtieth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation; and
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant,
the automatic gain control part switching the gain of the amplifier to a large value until the field synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal.
Preferably, as in a thirty-first aspect,
the amplifier is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a thirty-second aspect,
the amplifier is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
As described above, according to the thirtieth to thirty-second aspects, the amplitude gain of the automatic gain control part is switched to a large value until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a small value in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance.
A thirty-third aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the field synchronizing signal detected by the field synchronization detection part,
each of the automatic gain control part and the clock regeneration part switching the loop filter to a wide band until the field synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal.
Preferably, as in a thirty-fourth aspect,
the loop filter in each of the automatic gain control part and the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
each of the automatic gain control part and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a thirty-fifth aspect,
the loop filter in each of the automatic gain control part and the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
each of the automatic gain control part and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a thirty-sixth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to respectively control the bandwidths of the loop filters.
Preferably, as in a thirty-seventh aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to respectively control the bandwidths of the loop filters.
As described above, according to the thirty-third to thirty-seventh aspects, the loop filter in each of the automatic gain control part and the clock regeneration part is switched to a wide band until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a narrow band in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A thirty-eighth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the field synchronizing signal detected by the field synchronization detection part,
each of the automatic gain control part and the clock regeneration part switching the gain of the amplifier to a large value until the field synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal.
Preferably, as in a thirty-ninth aspect,
the amplifier in each of the automatic gain control part and the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
each of the automatic gain control part and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a fortieth aspect,
the amplifier in each of the automatic gain control part and the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
each of the automatic gain control part and the clock regeneration part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a forty-first aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to respectively control the gains of the amplifiers.
Preferably, as in a forty-second aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to respectively control the gains of the amplifiers.
As described above, according to the thirty-eighth to forty-second aspects, the amplitude gain of each of the automatic gain control part and the clock regeneration part is switched to a large value until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being switched to a small value in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A forty-third aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the field synchronizing signal detected by the field synchronization detection part,
the automatic gain control part switching the loop filter to a wide band until the field synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal, and the clock regeneration part switching the gain of the amplifier to a large value until the field synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the field synchronization detecting signal.
Preferably, as in a forty-fourth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a forty-fifth aspect,
the loop filter in the automatic gain control part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a forty-sixth aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the amplifier in the clock regeneration part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
Preferably, as in a forty-seventh aspect,
the loop filter in the automatic gain control part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and the amplifier in the clock regeneration part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and
the automatic gain control part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter, and the clock regeneration part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier.
As described above, as in the forty-third to forty-seventh aspects, the loop filter in the automatic gain control part and the amplitude gain of the clock regeneration part are respectively switched to a wide band and a large value until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being respectively switched to a narrow band and a small value in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.
A forty-eighth aspect is directed to a VSB receiver for receiving a terrestrial digital broadcasting signal obtained by subjecting video and audio data constructed in a format having a segment synchronizing signal at the head of each of segments and a field synchronizing signal at the head of each of fields to multi-valued VSB (octal or hexadecimal VSB) modulation and transmitted, characterized by comprising:
field synchronization detection part for detecting the field synchronizing signal from the received signal which has been subjected to the multi-valued VSB modulation;
automatic gain control part whose loop gain is feedback-controlled through a gain detector, an amplifier, and a loop filter on the basis of the field synchronizing signal detected by the field synchronization detection part such that the level of the field synchronizing signal is constant; and
clock regeneration part whose loop gain is feedback-controlled through a clock frequency detector, an amplifier, a loop filter, and a variable clock oscillator such that a clock frequency to be regenerated coincides with the clock frequency of the received signal on the basis of the field synchronizing signal detected by the field synchronization detection part,
the automatic gain control part switching the gain of the. amplifier to a large value until the field synchronizing signal is detected, while switching the gain of the amplifier to a small value after it is detected in accordance with the field synchronization detecting signal indicating the presence or absence of the detection of the field synchronizing signal, and the clock regeneration part switching the loop filter to a wide band until the field synchronizing signal is detected, while switching the loop filter to a narrow band after it is detected in accordance with the field synchronization detecting signal.
Preferably, as in a forty-ninth aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a fiftieth aspect,
the amplifier in the automatic gain control part is constituted by a high-gain operational amplifier and a low-gain operational amplifier, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the amplifier to either one of the operational amplifiers in accordance with the field synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a fifty-first aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the loop filter in the clock regeneration part is a wide-band loop filter and a narrow-band loop filter, each of which is constituted by a resistor and a capacitor, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the value of a time constant determined by the resistor and the capacitor in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
Preferably, as in a fifty-second aspect,
the amplifier in the automatic gain control part is a multiplier whose amplitude value can be varied in accordance with a coefficient separately given thereto, and the loop filter in the clock regeneration part is a digital filter whose bandwidth can be varied in accordance with a filter coefficient separately given thereto, and
the automatic gain control part switches the coefficient given to the multiplier in accordance with the field synchronization detecting signal, to control the gain of the amplifier, and the clock regeneration part switches the filter coefficient given to the digital filter in accordance with the field synchronization detecting signal, to control the bandwidth of the loop filter.
As described above, as in the forty-eighth to fifty-second aspects, the amplitude gain of the automatic gain control part and the loop filter in the clock regeneration part are respectively switched to a large value and a wide band until the field synchronizing signal is detected such that a time period required for the detection is shortened, while being respectively switched to a small value and a narrow band in order to improve a ghost disturbance removal performance after the field synchronizing signal is detected, to control the loop gain. Even when there is a ghost disturbance in the received signal, therefore, it is possible to shorten the time period required to detect the field synchronizing signal as well as to improve the ghost disturbance removal performance. Further, no jitter occurs in a regenerated clock in the VSB receiver, so that no error occurs in the received signal.